Nanostructure optoelectronic device having sidewall electrical contact

ABSTRACT

Nanostructure array optoelectronic devices are disclosed. The optoelectronic device may have a top electrical contact that is physically and electrically connected to sidewalls of the array of nanostructures (e.g., nanocolumns). The top electrical contact may be located such that light can enter or leave the nanostructures without passing through the top electrical contact. Therefore, the top electrical contact can be opaque to light having wavelengths that are absorbed or generated by active regions in the nanostructures. The top electrical contact can be made from a material that is highly conductive, as no tradeoff needs to be made between optical transparency and electrical conductivity. The device could be a solar cell, LED, photo-detector, etc.

CROSS-REFERENCE TO RELATED APPLICATIONS

The following applications are cross-referenced and incorporated byreference herein in their entirety:

U.S. patent application Ser. No. 12/796,589, entitled “Multi-JunctionSolar Cell Having Sidewall Bi-Layer Electrical Interconnect,” by Kim etal., filed on the same day as the present application; and

U.S. patent application Ser. No. 12/796,600, entitled “NanostructureOptoelectronic Device with Independently Controllable Junctions,” by Kimet al., filed on the same day as the present application.

FIELD

The present disclosure relates to optoelectronic devices.

BACKGROUND

Numerous types of optoelectronic devices that are based onsemi-conductor devices are known. For example, solar cells, lightemitting diodes (LEDs), imaging devices, and photo-detectors may bebased on semi-conductor devices. Such optoelectronic devices may beoperated by forward biasing, reverse biasing, or no biasing. Forexample, an LED may be operated by forward biasing a diode junction tocause light to be emitted. Some photo-detectors or imaging devices maybe operated by reverse biasing a diode junction (note that the diodejunction may not need to be reverse biased for detector operation).Solar cells, otherwise known as photo-voltaic cells, may be operatedwithout applying any bias. Instead, photons absorbed by photo-activeregions of the device generate voltage or/and current.

The foregoing illustrates that such optoelectronic devices need twoelectrical contacts. For many optoelectronic devices, the electricalcontacts are placed at opposite sides of the device, which may bereferred to as a top and bottom electrical contact, respectively.Moreover, at least one side of the optoelectronic device needs to beable to either receive or emit light, at least for a relevant range ofwavelengths. By a relevant range of wavelengths it is meant a range ofwavelengths that is either absorbed or emitted by the photo-activeregions.

For many optoelectronic devices, light is emitted or received throughthe top electrical contact. For such optoelectronic devices, a trade-offis made between optical transparency and electrical conductivity of thetop electrical contact. For example, the top electrical contact may bemade from a material that has good optical transparency, at least in therelevant range of wavelengths for the device. As one example, the topelectrical contact may be formed from indium-tin-oxide (ITO). However,optically transparent materials may not be as electrically conductive asdesired. Hence, operation of the device may suffer. For example, whenbeing operated as a solar cell, greater resistance of the top electricalcontact results in greater voltage drop across the top electricalcontact. On the other hand, electrically conductive materials may not beas optically transparent as desired.

Note that some materials that may be used for top electrical contactsare optically transparent for a relatively narrow range of wavelengths.Therefore, they may be suited for optoelectronic devices that areintended to be operated over a narrow range of wavelengths. However, itmay be desirable to operate the device over a wider range ofwavelengths. For example, it may be desirable to operate a solar cellover a wide range of wavelengths in order to capture energy presentacross a wide range the solar spectrum. It may be desirable to operatesome LED devices over a wide range of wavelengths also. For example, itmay be desirable to have an LED device that can produce light ofdifferent colors. Also, imaging devices should be able to detectdifferent colors.

Therefore, improvements are desired in the electrical contacts foroptoelectronic devices.

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1A depicts one embodiment of an optoelectronic device having a topsidewall electrical contact.

FIG. 1B depicts one embodiment of an optoelectronic device having a topsidewall electrical contact.

FIG. 2A is a side sectional perspective view of one embodiment of anoptoelectronic device having a top sidewall electrical contact.

FIG. 2B depicts an embodiment in which a portion of the photo-activeregion extends above a top sidewall electrical contact.

FIG. 2C is a side sectional perspective view of one embodiment of anoptoelectronic device having a top sidewall electrical contact.

FIG. 3A depicts one embodiment of an optoelectronic device having anintermediate sidewall electrical contact.

FIG. 3B depicts a side perspective cross-sectional view of oneembodiment of an optoelectronic device having an intermediate sidewallelectrical contact.

FIG. 3C depicts one embodiment of an optoelectronic device having threesidewall electrical contacts and exposed edges.

FIG. 4A depicts one embodiment of an optoelectronic device having abi-layer sidewall electrical interconnect.

FIG. 4B depicts a side sectional view of an optoelectronic device havinga bi-layer sidewall electrical interconnect.

FIG. 4C depicts an example circuit schematic of one possible operationof the device of FIG. 4B.

FIG. 5A is a flowchart depicting one embodiment of a process offabricating an optoelectronic device having one or more sidewallelectrical contacts.

FIG. 5B is a flowchart depicting one embodiment of a process offabricating a sidewall electrical contact.

FIG. 5C is a flowchart depicting one embodiment of a process offabricating a sidewall electrical contact using angle deposited metal.

FIG. 5D is a flowchart depicting one embodiment of a process offabricating an optoelectronic device that has at least one bi-layersidewall electrical interconnect.

FIG. 6A and FIG. 6B show results after various steps in one embodimentof the process of FIG. 5A.

FIG. 6C, FIG. 6D, FIG. 6E, FIG. 6F, FIG. 6G, and FIG. 6H show resultsafter various steps in one embodiment of the process of FIG. 5B.

FIG. 7A, FIG. 7B, and FIG. 7C depict side section perspective views ofthe device of FIGS. 3A and 3B.

FIG. 8A is a flowchart of one embodiment of a process of independentlycontrolling different photo-active junctions of an optoelectronicdevice.

FIG. 8B is a flowchart of one embodiment of a process of independentlycontrolling different photo-active junctions of an optoelectronicdevice.

FIG. 8C is a flowchart of one embodiment of a process of independentlycontrolling different photo-active junctions of an optoelectronicdevice.

FIG. 9 depicts one embodiment of a process of fabricating anoptoelectronic device that has active regions in a nanostructure arraythat can be independently controlled.

FIG. 10A depicts one embodiment of a pixilated nanostructureoptoelectronic device.

FIG. 10B depicts a side cross sectional perspective view of a portion ofthe device of FIG. 10A.

FIG. 10C depicts one embodiment of a biasing scheme for a pixilateddevice.

FIG. 10D shows one example biasing scheme for photo-detector operationfor a pixilated device such as the example devices depicted in FIGS. 10Aand 10B.

FIG. 11 depicts a flowchart of embodiment of a process of operating anoptoelectronic device.

FIG. 12A, FIG. 12B, and FIG. 12C depict one embodiment of a biasingscheme for LED operation in which different color sub-pixels areoperated simultaneously.

FIG. 12D shows one possible biasing scheme for selecting two differentcolors of sub-pixels in the same nanostructure for photo-detectoroperation.

FIGS. 13A, 13B, 13C, 13D, 13E, 13F, 13G, and 13H depict one embodimentof a biasing scheme in which three different color sub-pixels areoperated simultaneously for LED operation.

FIG. 13I depicts one embodiment of a biasing scheme in which threedifferent color sub-pixels are operated simultaneously forphoto-detector operation.

FIG. 14 depicts one embodiment of a process of fabricating a pixilatedoptoelectronic device.

FIG. 15A is a diagram of one embodiment of a pixilated nanostructureoptoelectronic device.

FIG. 15B is a side perspective view of the device of FIG. 15A.

FIG. 16 is a block diagram of one embodiment of a computing system foruse with embodiments of technology disclosed herein.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however,that embodiments may be practiced without these specific details. Inother instances, well-known structures and devices are shown in blockdiagram form in order to avoid unnecessarily obscuring the disclosure.

Optoelectronic devices having photo-active regions (“active regions”)are disclosed herein. The optoelectronic device comprisesnanostructures, in some embodiments. The nanostructures may benanocolumns, nanowires, nanorods, nanotubes, etc. In some embodiments,the nanostructures are grouped in an array. For example, thenanostructures may be grown vertically on a substrate. However, thenanostructures could also be formed from the top down by patterning astack of planar layers and subsequent etching. The nanostructures may beformed from a variety of materials. In some embodiments, thenanostructures are formed from one or more semiconductors.

Optoelectronic devices described herein may be used for solarphoto-conversion devices (also referred to as solar cells),photo-detectors (also referred to as light detectors), imaging devices,monochrome LEDs, multi-constituent color LEDs, spectrometers, and otherdevices not specifically mentioned.

In some embodiments, the optoelectronic device has a top electricalcontact that is physically and electrically connected to sidewalls ofthe array of nanostructures (e.g., nanocolumns). The top electricalcontact may be located such that light can enter or leave thenanostructures without passing through the top electrical contact.Therefore, the top electrical contact can be opaque to light havingwavelengths that are absorbed or generated by active regions in thenanostructures. Moreover, the top electrical contact can be made from amaterial that is highly conductive, as no tradeoff needs to be madebetween optical transparency and electrical conductivity.

In some embodiments, the optoelectronic device has one or moreintermediate electrical contact that are physically and electricallyconnected to sidewalls of the array of nanostructures. The contacts mayallow different photo-active regions of the optoelectronic device to beindependently controlled. For example, a top and intermediate electricalcontact can be used to control an upper photo-active regions and theintermediate and bottom electrical contact may be used to control lowerphoto-active regions. Note that each nanostructure may have one of thelower- and one of the upper photo-active regions.

In some embodiments, the optoelectronic device has a bi-layer electricalinterconnect that is physically and electrically connected to sidewallsof the array of nanostructures. The optoelectronic device may beoperated as a multi junction solar cell, wherein each junction isassociated with one portion of the device. The bi-layer electricalinterconnect allows current to pass from one portion to the next. Thus,the bi-layer electrical interconnect may serve as a replacement for atunnel junction, which is used in some conventional multi junction solarcells.

In some embodiments, the optoelectronic device is a pixilated devicethat may serve as an LED display or imaging sensor, for example. Theoptoelectronic device may have an array of nanostructures withalternating rows and columns of sidewall electrical contacts atdifferent layers. In this embodiment, the electrical contacts may belong strips. This allows a group of one or more nanostructures to serveas a pixel having sub-pixels. For example, a pixel may be formed at theintersection of a row contact and a column contact. In some embodiments,a single group of one or more nanostructures has a blue sub-pixel, agreen sub-pixel, and a red sub-pixel. Each pixel may have any number ofsub-pixels.

Nanostructure Array Optoelectronic Device with Top Sidewall ElectricalContact

FIG. 1A depicts one embodiment of an optoelectronic device 100 having atop sidewall electrical contact 104 a. In one embodiment, theoptoelectronic device 100 is a solar cell. In one embodiment, theoptoelectronic device 100 is an LED. In one embodiment, theoptoelectronic device 100 is a photo-detector. For example, the device100 may be a single junction solar cell. In other embodiments, thedevice 100 has multiple junctions. The example device 100, in general,comprises an array of nanostructures 96, a top sidewall electricalcontact 104 a, a substrate 108, a bottom electrical contact 102, anoptional window 105, and electrical leads 112. Note that the topsidewall electrical contact 104 a and the bottom electrical contact 102may be externally accessible.

Each of the nanostructures 96 may have one or more photo-active regions(not depicted in FIG. 1A). Each of the nanostructures 96 has a top, abottom, and sidewalls. In one embodiment, the lateral width of thenanostructures 96 may range from about 5 nm-500 nm. However,nanostructures 96 may have a lesser or greater lateral width. The entirerange of widths may be present in a single device. Thus, there may beconsiderable variance in width of individual nanostructures 96. Alsonote that the width of an individual nanostructures 96 may vary from topto bottom. For example, a nanostructure 96 could be narrower, or wider,at the top. Also note that nanostructures 96 are not necessarilycolumnar in shape. As depicted, there are spaces or gaps between thenanostructures 96. These spaces may be filled with an insulator;however, the spaces may also be left open such that there may be an airgap between nanostructures 96. The nanostructures 96 are not coalesced,in some embodiments. That is to say, that individual nanostructures 96are not required to be joined together laterally at some level. Forexample, in some conventional devices the nanostructures 96 arecoalesced at the tops such that a continuous sheet is formed. Note thatalthough each nanostructure 96 is depicted in FIG. 1A as completelyseparate from others, some of the nanostructures 96 might touch aneighbor at some point on the sidewalls.

The nanostructures 96 may include one or more segments. A given segmentmay be p-doped, n-doped, co-doped, or intrinsic (not intentionallydoped) for various purposes including, but not limited to, creatingphoto-active junctions. A segment may be heavily doped to create atunnel junction. Different segments may be formed from differentmaterials. For example, different segments may be formed from differentmaterials such that different photo-active junctions emit or detectlight different wavelengths of light. As another example, thenanostructures 96 may be formed from a material that comprises a III-Vcompound semiconductor and an element that alters the band gap of theIII-V compound semiconductor, such an indium. Different segments mayhave different amounts of indium in order to create energy wells.Further details of solar cells having nanostructures 96 with energywells are described in U.S. Pat. No. 7,629,532, filed on Dec. 29, 2006,titled “Solar Cells having Active Region with Nanostructures havingEnergy Wells,” which is hereby incorporated by reference in itsentirety.

The top sidewall electrical contact 104 a is in electrical and physicalcontact with the sidewalls near the tops of the nanostructures 96.However, the top sidewall electrical contact 104 a leaves a top portion96 a of the nanostructures 96 exposed to allow light to enter or leavethe nanostructures 96 from the tops 96 a without passing through the topelectrical contact 104 a. Therefore, the top electrical contact 104 amay be substantially opaque to light having a wavelength that isabsorbed or generated by the photo-active regions. The top sidewallelectrical contact 104 a has a substantially planar structure in someembodiments. However, note that the thickness of the top sidewallelectrical contact 104 a is allowed to vary. Note that the top sidewallelectrical contact 104 a may be formed substantially around thesidewalls of each of the nanostructures 96. The top electrical contact104 a may completely fill the spaces between the nanostructures 96 at alevel near the tops 96 a of the nanostructures 96.

The top electrical contact 104 a may be formed from a different materialthan the nanostructures 96. In some embodiments, the top sidewallelectrical contact 104 a is formed from a metal. Example metals include,but are not limited to, nickel and aluminum. Therefore, the top sidewallelectrical contact 104 a may have a very high conductivity. For example,the top electrical contact 104 a may have a higher electricalconductivity than the nanostructures 96; although this is not required.In some embodiments, the top electrical contact 104 a forms an Ohmiccontact with the nanostructures 96. Therefore, a good electricalconnection may be made to the nanostructures 96. In some embodiments,the top electrical contact 104 a forms a Schottky contact with thenanostructures 96.

The optional window 105 allows light to enter or leave the device 100.The window 105 protects the device 100 and may passivate the topsurface. The window 105 may be formed from a material that is highlytransparent to light of the relevant wavelengths. Because the window 105does not need to pass an electrical current, the window 105 does notneed to be electrically conductive. Therefore, no tradeoff betweenoptical transparency and electrical conductivity needs to be made forthe window 105. Note that another material, such as an insulator, may bepresent between the window 105 and the top electrical contact 104 a.

Examples of suitable materials for the substrate 108 include, but arenot limited to, Si, germanium (Ge), silicon carbide (SiC), zinc oxide(ZnO), and sapphire. If the substrate 108 is either Si, or Ge, thesubstrate 108 may be (111) plane oriented, as one example. If thesubstrate 108 is SiC, or ZnO, the substrate 108 may be (001) planeoriented, as one example. The substrate 108 is doped with a p-typedopant, in one embodiment. An example of a p-type dopant for Sisubstrates includes, but is not limited to, boron (B). The p-type dopinglevel may be p, p⁺ or, p⁺⁺. The substrate 108 is doped with an n-typedopant, in one embodiment. Examples of n-type dopants for Si substratesinclude, but are not limited to, arsenic (As) and phosphorous (P). Then-type doping level may be n, n⁺ or, n⁺⁺. Note that the substrate 108 isnot required for device operation. In some embodiments, the substrate108 on which the nanostructures 96 were grown is removed (e.g., byetching), which allows for a more flexible device.

The bottom electrical contact 102 may be made of a suitable metal, anddoes not need to be optically transparent. The bottom electrical contact102 is electrically connected to the nanostructures 96. In someembodiments, the bottom electrical contact 102 is in physical contactwith the sidewalls of the nanostructures 96; however, sidewall contactis not required. Thus, the bottom electrical contact 102 may, or may notbe, a sidewall electrical contact. As depicted in FIG. 1A, the bottomelectrical contact 102 is attached to the back side (or bottom) of thesubstrate 108. As mentioned, the substrate 108 may be doped such that itis conductive. If desired, portions of the substrate 108 may be etchedaway and filled with a conductive material, such as a metal, to allow abetter conductive contact between the bottom electrical contact 102 andthe nanostructures 96. As mentioned, the substrate 108 is not anabsolute requirement. In this case, the bottom electrical contact 102may be bonded to the nanostructures 96. In one embodiment, the bottomelectrical contact 102 is between the substrate 108 and thenanostructures 96 (but is not a sidewall contact).

Overview of operation of an embodiment in which the device 100 is asolar cell will now be discussed. Solar radiation (e.g., photons) entersthrough the window 105 and into the top portions 96 a of nanostructures96 and may be absorbed in the active regions (not explicitly depicted inFIG. 1A) of nanostructures 96. Absorption of a photon promotes anelectron to the conduction band. Electrons promoted to a conduction bandby the absorption of photons may conduct to the electrical contacts 104a, 102. The electrons conduct through the electrical leads 112.Typically, a bias voltage is not applied to the device 100 when beingoperated as a solar cell.

Overview of operation of an embodiment in which the device 100 is an LEDwill now be discussed. A bias voltage is applied through the leads 112to forward bias a p-n junction (not depicted in FIG. 1A) in thenanostructures 96, resulting in emission of photons through the topportions 96 a of the nanostructures 96 and out the window 105 (note thatthe window 105 is optional). Note that the emitted photons need not passthrough the top sidewall electrical contact 104 a.

Overview of operation of an embodiment in which the device 100 is aphoto-detector or imaging device will now be discussed. A bias voltagemay be applied through the leads 112 to reverse bias a p-n junction (notdepicted in FIG. 1A) in the nanostructures 96. Photons that enterthrough the window 105 (if present) are absorbed in the photo-activeregions of the nanostructures 96, which promotes electrons to theconduction band. Electrons promoted to the conduction band may conductto the contacts 104 a, 102 and through the electrical leads 112. Theamount of current that conducts may be detected to determine theintensity of light at the relevant wavelength of the photo-activejunctions. In some embodiments, a bias voltage is not applied to thedevice 100 when being operated as a photo-detector or imaging device.

Thus, electrical conduction may occur along the length of nanostructures96 for the various optoelectronic devices. For example, electricalconduction may occur along the length of nanocolumns. Note that thedevice 100 may be used for other devices than the examples provided.

Note that a portion of the sidewalls of the nanostructures 96 is notrequired to be above the top sidewall electrical contact 104 a. FIG. 1Bdepicts one embodiment of an optoelectronic device 110 having a topsidewall electrical contact 104 a. In this embodiment, no portion of thesidewalls of the nanostructures 96 is above the top sidewall electricalcontact 104 a. However, top portions 96 a of the nanostructures 96 areexposed to allow light to enter or leave the nanostructures 96 a fromthe tops 96 a without passing through the top electrical contact 104 a.Note that the top sidewall electrical contact 104 a may completely fillthe spaces between the nanostructures 96 at a level near the tops 96 aof the nanostructures.

FIG. 2A depicts a side cross sectional showing one embodiment of how thetop sidewall electrical contact 104 a is in physical contact with thesidewalls of the nanostructures 96. In this embodiment, the device 100has a p-n junction and active region associated therewith. The topsidewall electrical contact 104 a is electrically and physicallyconnected to the p-type regions of the nanostructures 96. However, notethat the top electrical contact 104 a may instead be in contact with ap-doped region, n-doped region, intrinsic region, or co-doped region. Insome embodiments, the material for the top sidewall electrical contact104 a is selected such that it makes a good Ohmic contact with the typeof material (e.g., semiconductor and type of doping) of thenanostructures 96 that it contacts. However, other contacts such as aSchottky contact are also possible.

The bottom electrical contact 102 is electrically connected to then-type regions of the nanostructures 96. The bottom electrical contact102 may be in physical contact with the sidewalls of the nanostructures96; however, that is not required. In another embodiment, the n-type andp-type regions are switched, such that the top sidewall electricalcontact 104 a is electrically and physically connected to an n-typeregion. In some embodiments, there is an intrinsic region between thep-type region and n-type region. In some embodiments, each of thenanostructures 96 has a photo-active region associated with the p-njunction. The extent of one example photo-active region is depicted;however, it will be appreciated that the extent of the photo-activeregion does not necessarily have fixed boundaries.

Also, note that in some embodiments, a portion of the photo-activeregion may extend above the top sidewall electrical contact 104 a. FIG.2B depicts such an embodiment. In some embodiments, the top surface ofthe top electrical contact 104 a is at least partially reflective tolight of relevant wavelengths such that incoming light that is notdirectly received by one of the nanostructures 96 is reflected off fromthe top electrical contact 104 a and into the sidewalls of thenanostructures 96 above the top electrical contact 104 a. Therefore,this reflected light may be absorbed by the photo-active region abovethe top electrical contact 104 a.

Note that the tops 96 a of the nanostructures do not necessarily have aflat surface at the very top. For example, one or more of thenanostructures 96 may have a point or rounded top. FIG. 2C is a sidesectional perspective view of one embodiment of an optoelectronic device100 in which the tops 96 a are not flat. In this example, the tops 96 aare somewhat pointed. The tops 96 a may have other shapes. The tops 96 aextend above the top electrical contact 104 a such that light may enteror leave the nanostructures 96 through the tops 96 a without passingthrough the top electrical contact 104 a.

In the embodiment of FIG. 2C, the device 250 has a p-n junction. Thedevice may have a p-i-n junction instead. The top sidewall electricalcontact 104 a is electrically and physically connected to the p-typeregions of the nanostructures 96 in this example. However, note that thetop electrical contact may instead be in contact with a p-doped region,n-doped region, intrinsic region, or co-doped region. In someembodiments, the material for the top contact 104 a is selected suchthat it makes a good Ohmic contact with the type of material (e.g.,semiconductor and type of doping) of the nanostructures 96 that itcontacts. However, other contacts such as a Schottky contact are alsopossible.

Note that in the devices of FIGS. 2A, 2B and 2C the top sidewallelectrical contact 104 a and the bottom electrical contact 102 may beexternally accessible by attaching electrical leads 112 to the contacts.

Nanostructure Array Optoelectronic Device with Intermediate SidewallElectrical Contacts

Note that the optoelectronic device may have one or more intermediatesidewall electrical contacts. By an intermediate sidewall electricalcontacts it is meant an electrical contact that is neither a topelectrical contact nor a bottom electrical contact and is physicallytouching sidewalls of the nanostructures 96. Therefore, the device hasmore than two electrical contacts in these embodiments. For example, thedevice may have three, four, or more electrical contacts.

FIG. 3A depicts one embodiment of an optoelectronic device 300 havingthree sidewall electrical contacts 104 a, 104 b, 104 c. Specifically,the device 300 has a top sidewall electrical contact 104 a, anintermediate sidewall electrical contact 104 c, and a bottom sidewallelectrical contact 104 b, in this embodiment. Note that each contact mayhave an electrical lead 112 attached to it such that a voltage orcurrent may be provided or received.

Note that the bottom electrical contact is not required to be on thesidewalls. For example, it could be below the substrate 108 or attachedto the bottoms of the nanostructures 96. Moreover, the top electricalcontact is not required to be on the sidewalls. For example, it could beattached to the tops of the nanostructures 96. Other elements of thedevice 300 (such as leads, insulation, front window) are not depicted soto not obscure the diagram.

FIG. 3B depicts a side perspective cross-sectional view of oneembodiment of an optoelectronic device 300 having an intermediatesidewall electrical contact 104 c. The device is similar to the onedepicted in FIG. 3A and also has a top sidewall electrical contact 104 aand a bottom sidewall electrical contact 104 b. Electrical leads 112 arenot explicitly depicted, but may be attached to each electrical contact.FIG. 3B depicts an example in which each of the nanostructures 96 has,from top to bottom, an n-type region 302, a p-type region 304 and ann-type region 306. Therefore, the device has first and secondphoto-active regions (which are roughly depicted) associated with thetwo p-n junctions. Note that there could be intrinsic regions betweenthe n-type regions and p-type regions.

Each photo-active region may have different bandgap energy. Therefore,each photo-active region may emit or detect light of a different rangeof wavelengths. Alternatively, the device could have a p-type region, ann-type region, and a p-type region. Thus, in general, the nanostructures96 each have an upper and lower region having one type of conductivityand a middle region having the opposite type of conductivity.

In this example, the top sidewall electrical contact 104 a makeselectrical and physical contact with upper n-type semiconductor regionsof the nanostructures 96, the intermediate sidewall electrical contact104 c makes electrical and physical contact with p-type semiconductorregions of the nanostructures 96, and the bottom sidewall electricalcontact 104 b makes electrical and physical contact with lower n-typesemiconductor regions of the nanostructures 96.

In some embodiments, the sidewall contacts 104 a-104 c each make Ohmiccontact with their region. Thus, sidewall contacts 104 that contact then-type semiconductor regions may be made of a suitable material to forman Ohmic contact with an n-type semiconductor. Sidewall contacts 104that contact the p-type semiconductor regions may be made of a suitablematerial to form an Ohmic contact with a p-type semiconductor. Herein,the term “n-type” contact will refer to a material that forms an Ohmiccontact with an n-type semiconductor. Herein, the term “p-type” contactwill refer to a material that forms an Ohmic contact with a p-typesemiconductor.

FIG. 3C depicts one embodiment of an optoelectronic device 300 havingthree sidewall electrical contacts and exposed edges. The device 300 issimilar to the ones depicted in FIGS. 3A and 3B. Two layers ofinsulation 325 are depicted between the contacts. FIG. 3C only depicts asmall portion of the device 300 near one edge. The device 300 has acontact pad 1032 attached to each electrical contact 104 and anelectrical lead 112 attached to each electrical contact 104. Controllogic 725 connects to the leads 112. The control logic 725 may be usedto independently control different photo-active regions in thenanostructures 96. Further details are discussed below. The edges can beexposed using a wide variety of techniques such as photolithography andetching.

Bi-Layer Nanostructure Sidewall Electrical Interconnect

In some embodiments, the optoelectronic device has a bi-layer sidewallelectrical interconnect. A bi-layer sidewall electrical interconnect mayinclude an n-type contact and a p-type contact. Therefore, the bi-layersidewall electrical interconnect may make contact to both n-typesemiconductor regions and p-type semiconductor regions of thenanostructures 96.

FIG. 4A depicts one embodiment of an optoelectronic device 400 having abi-layer sidewall electrical interconnect 104 d. The optoelectronicdevice 400 also has a top sidewall electrical contact 104 a and a bottomsidewall electrical contact 104 b. However, top and bottom electricalcontacts are not required to be on the sidewalls of the nanostructures96. The bi-layer sidewall electrical interconnect 104 d includes a toplayer 404 a and a bottom layer 404 b. As mentioned, one layer is ann-type contact, and the other is a p-type contact. Either layer may ben-type contact, depending on the doping of the nanostructures 96.

In some embodiments, the optoelectronic device 400 of FIG. 4A is amulti-junction solar cell. The device 100 may have a first lead 112electrically connected to the top sidewall electrical contact 104 a anda second lead 112 electrically connected to the bottom sidewallelectrical contact 104 b. However, as will be explained below, thedevice 100 does not necessarily have electrical leads 112 connected tothe bi-layer sidewall electrical interconnect 104 d.

FIG. 4B depicts a side sectional perspective view of an optoelectronicdevice 400 having a bi-layer sidewall electrical interconnect 104 d. Thedevice is similar to the one of FIG. 4A. Note that in this example thenanostructures 96 have p-type regions 452, n-type regions 454, p-typeregions 456, and n-type regions 458. In this example, the top layer 404a of bi-layer sidewall electrical interconnect 104 d contacts n-typeregions 454 and the bottom layer 404 b of bi-layer sidewall electricalinterconnect 104 d contacts p-type regions 456. In one embodiment, thelayer 404 a makes Ohmic contact with the n-type regions. For example,layer 404 a may be aluminum and the nanostructures 96 may be nitridesemiconductors. In one embodiment, layer 404 b makes Ohmic contact withthe p-type regions. For example, layer 404 b may be nickel and thenanostructures 96 may be nitride semiconductors. The top sidewallelectrical contact 104 a contacts the top p-type regions 452 and thebottom sidewall electrical contact 104 b contacts the lower n-typeregions 458. Note that the p-type and n-type regions could be reversed.

Also note that the junction between the top layer 404 a and bottom layer104 b does not need to be perfectly aligned with the p-n junction ofregions 454 and 456. A reason for this is that, in some embodiments, agiven layer of the bi-layer interconnect 104 d only makes Ohmic contactwith semiconductor of the correct conductivity type. For example, toplayer 404 a may be in physical contact with part of p-type region 456(as well as n-type region 454). In this case, top layer 404 a will stillhave Ohmic contact with the n-type region 454 and the bottom layer 404 bwill still have Ohmic contact with the p-type region 456. However, thetop layer 404 a should not have Ohmic contact with the p-type region 456even if there is some physical contact. Similarly, bottom layer 404 bmay be in physical contact with part of n-type region 454 (as well asp-type region 456). In this case, bottom layer 404 b will still haveOhmic contact with the p-type region 454 and the top layer 404 a willstill have Ohmic contact with the n-type region 454. However, the bottomlayer 404 b should not have Ohmic contact with the n-type region 454even if there is some physical contact.

As mentioned, the optoelectronic device 400 of FIGS. 4A and 4B may be amulti junction solar cell. The p-n junction between p-type regions 452and n-type regions 454 may operate as a first p-n junction, whereas thep-n junction between p-type regions 456 and n-type regions 458 mayoperate as a second p-n junction. Note that p-i-n junctions are alsopossible. The bi-layer sidewall electrical interconnect 104 d may allowcharge to flow between the n-type regions 454 and the p-type regions 456through the bi-layer electrical interconnect. Each p-n junction may havedifferent bandgap energy. Therefore, the active region associated witheach p-n junction may emit or detect light of a different range ofwavelengths.

FIG. 4C depicts an example circuit schematic of one possible operationof the device 400 of FIGS. 4B. The optoelectronic device 400 may beconsidered to be two diodes 462 a 462 b that are connected by thebi-layer sidewall electrical interconnect 104 d. Current that isgenerated by absorption of photons may flow from the upper diode 462 ato the upper portion 404 a of the bi-layer interconnect 104 d, then tothe lower portion 404 b of the bi-layer interconnect 104 d. Then, thecurrent flows through the lower diode 462 b and into the lower lead 112.The upper lead 112 a completes the circuit. Note that somemulti-junction solar cell have a tunnel junction between diodes.However, tunnel junctions are sometimes difficult to form. The bi-layer104 d sidewall electrical interconnect may thus serve as a replacementfor a tunnel junction.

Fabricating a Nanostructure Array Optoelectronic Device Having One orMore Sidewall Electrical Contacts

FIG. 5A is a flowchart depicting one embodiment of a process 500 offabricating an optoelectronic device that has one or more sidewallelectrical contacts. Process 500 may be used to fabricate a device suchas those depicted in FIGS. 1A, 1B, 2A, 2B, 2C, 3A, 3B, 4A, and 4B.However, process 500 is not limited to fabricating those devices. Notall process steps are depicted so as to simplify the explanation. FIGS.6A-6B show results after various steps in one embodiment of process 500.FIGS. 6A-6B show a side perspective view showing a cutaway portion of afew nanostructures 96.

In step 502, nanostructures 96 are formed. In one embodiment, an arrayof nanostructures 96 are grown vertically on a substrate 108. Thenanostructures 96 may be grown either by self-assembly or by patternedgrowth using epitaxial growth techniques such as metalorganic chemicalvapor deposition, molecular beam epitaxy and hydride vapor phaseepitaxy. In patterned growth, a portion of the substrate surface whichis not covered by mask material such as SiO₂, SiN_(x), or metal isexposed to serve as nucleation sites for the nanostructures 96. Thenanostructures 96 may also be grown using nanoparticles such as gold(Au) and nickel (Ni), which may act as nucleation sites for thenanostructures 96.

In some embodiments the nanostructures 96 are formed by patterning andetching. For example, one or more planar layers of material for thenanostructures 96 is deposited. Each layer may be doped appropriately insitu or by implantation. After depositing and doping all layers,photolithography may be used to pattern and etch in order to form thenanostructures 96.

In some embodiments, the nanostructures 96 are doped with one or moreimpurities to create one or more p-type semiconductor regions and one ormore n-type semiconductor regions. Intrinsic regions may also be formed.Note that the substrate 108 may be doped prior to forming thenanostructures 96. FIG. 6A depicts results after step 502. Specifically,a few nanostructures 96 out of an array of nanostructures 96 aredepicted over a substrate 108.

In step 504, a bottom electrical contact (102, 104 b) is formed. In oneembodiment, the bottom electrical contact surrounds the sidewalls of thenanostructures 96. In such embodiments, the bottom electrical contact104 b may be formed by depositing a material over the substrate 108(after the nanostructures 96 have been formed) and etching back thematerial. The material may be metal. In patterned growth employingconductive material (such as metal) as mask material, the mask layer mayserve as a bottom sidewall electrical contact 104 b. However, it is notrequired that the bottom electrical contact is a sidewall electricalcontact. FIG. 6B depicts results after step 504 for an embodiment inwhich the bottom electrical contact is a sidewall contact 104 b. Forsome embodiments, the bottom electrical contact may be added below thesubstrate 108 later.

In step 505, one or more intermediate sidewall electrical contacts 104 care formed. In step 506, a top sidewall electrical contact 104 a isformed. Further details of steps 505 and 506 are discussed below. Notethat for some devices both steps 505 and 506 are performed. For otherdevices, only one of steps 505 and 506 is performed.

FIG. 5B is a flowchart depicting one embodiment of a process 520 offabricating a sidewall electrical contact for an optical device that hasone or more sidewall electrical contacts. Process 520 is one embodimentof step 506 of FIG. 5A. Process 520 may also be used for step 505 ofFIG. 5A. FIGS. 6C-6H show results after various steps in one embodimentof the process of FIG. 5B. FIGS. 6C-6H show a side perspective viewshowing a cutaway portion of a few nanostructures 96 and continue fromthe processing depicted in FIGS. 6A-6B. However, note that it is notthat the bottom electrical contact be a sidewall electrical contact asdepicted in the FIGS. 6B-6H.

In step 507, an insulator is formed around the sidewalls of thenanostructures 96 above the substrate 108 (and above the bottom sidewallelectrical contact 104 b, if formed). In one embodiment, spin-on-glass(SOG) is applied. In one embodiments, silicon dioxide is sputtered. Inanother embodiment, photoresist is added. Note that more than one typeof material could be used. For example, layers of different materialscould be deposited or a single layer could include multiple materials.After depositing, the insulator is etched back to expose tops 96 a ofthe nanostructures 96. Note that the insulator may serve purposes suchas passivating the nanostructures 96, or modifying the electrical oroptical properties of the nanostructures 96. FIG. 6C depicts resultsafter step 507 showing the insulator 602 surrounding the nanostructuresidewalls.

In step 508, metal is deposited over the insulator 602 such that itsurrounds the nanostructure sidewalls. At this stage, portions of themetal might cover the tops of the nanostructure. FIG. 6D depicts resultsafter step 508 in which metal 604 forms a conformal layer around andover the tops of the nanostructures 96.

In step 510, a layer of photoresist, SOG, or other planarizing materialis formed over the metal 604 and planarized. FIG. 6E depicts resultsafter step 510 showing planarizing material 606 over the metal 604.

In step 512, the planarizing material 606 is etched back to reveal topsof nanostructures 96 covered with the metal 604. FIG. 6F depicts resultsafter step 512 showing that the planarizing material 606 has been etchedback to reveal portions of the metal 604 over the tops of thenanostructures 96. However, some of the planarizing material 606 remainsin regions between the nanostructures 96.

In step 514, the metal 604 is etched back with the remaining protectiveplanarizing material 606 in place in order to reveal tops ofnanostructures 96. In step 516, the planarizing material 606 is removed.FIG. 6G depicts results after step 516. FIG. 6G shows that the tops ofthe nanostructures 96 are exposed.

In step 518, the metal 604 is etched back to a position that leaves topsof the nanostructures 96 exposed. FIG. 6H depicts results after step 518showing the top sidewall electrical contact 104 a.

Note that steps similar to steps 507-518 may be performed to form metalcontacts at other levels. For example, steps similar to steps 507-518may be used for form an intermediate sidewall electrical contact. Thus,the process 520 may also be used for step 505 of FIG. 5A. Note that morethan one intermediate sidewall electrical 104 c contact may be formed.

FIG. 5C is a flowchart depicting one embodiment of a process 550 offabricating a sidewall electrical contact for an optoelectronic device100 that has one or more sidewall electrical contacts. Process 550 isone embodiment of step 506 of FIG. 5A. Not all process steps aredepicted so as to simplify the explanation. In this embodiment, aninsulating layer is not formed around the nanostructures 96. However, aninsulating layer may be formed, if desired.

In step 552, metal is angle deposited such that it surrounds thenanostructure sidewalls at the tops. The metal should coalesce such thata continuous region of metal is formed at the tops of the nanostructurearray. Note that the device may be rotated during the angle depositionin order to coat all sidewalls of the nanostructures at the top withmetal. The angle of deposition may be selected in order to control thedepth of the metal (e.g., how far down the sidewalls of thenanostructures that the metal extends).

Next steps 510-518 may be performed in order to etch the metal. Steps510-518 may be similar to steps 510-518 of FIG. 5B and will not bediscussed in detail.

FIG. 5D is a flowchart depicting one embodiment of a process 580 offabricating an optoelectronic device that has at least one bi-layerelectrical interconnect. Process 580 may be used to fabricate a devicesuch as those depicted in FIGS. 4A and 4B. However, process 580 is notlimited to fabricating those devices. Not all process steps are depictedso as to simplify the explanation. In step 582, nanostructures 96 areformed. Step 582 is similar to step 502 of FIG. 5A. The nanostructuresmay have first regions of a first conductivity type and second regionsof a second conductivity type to form first p-n junctions. Thenanostructures may have third regions of the first conductivity type andfourth regions of the second conductivity type to form second p-njunctions.

In step 584, a bottom electrical contact (102, 104 b) is formed. Formingbottom contacts has been discussed in connection with FIG. 5A

In step 586, one or more bi-layer sidewall electrical interconnects 104d are formed. The bi-layer sidewall electrical interconnect 104 d mayhave a first material in electrical and physical contact with the secondregions and a second material in electrical and physical contact withthe third regions. The first material and the second material may be inelectrical contact with each other to allow charge to flow between thesecond regions and the third regions through the bi-layer electricalinterconnect.

Forming the lower portion 404 b of the bi-layer interconnect 104 d maybe similar to forming an intermediate sidewall contact, which hasalready been discussed. After forming the lower portion 404 b, metal maybe deposited for the upper portion 404 a and etched back. In someembodiments, forming the upper portion 404 a is similar to the processfor forming an intermediate sidewall contact.

In step 588, a top sidewall electrical contact 104 a is formed, whichhas already been discussed. Note that the top contact is not required tobe a sidewall contact.

Independently Controlling Different Photo-active Junctions

In some embodiments, different photo-active junctions of theoptoelectronic device are controlled independently. In some embodimentsa device 300 such as the embodiment depicted in FIGS. 3A and 3B has itsjunctions independently controlled. FIGS. 7A, 7B, and 7C depict a sidesectional perspective view of a portion of the device of FIGS. 3A and 3Bwith control logic 725 that independently controls differentphoto-active junctions. The device 300 has a first photo-active junction703 formed by n-type semiconductor region 302 and p-type semiconductorregion 304. The device 300 has a second photo-active junction 705 formedby p-type semiconductor region 304 and n-type semiconductor region 306.Note that only one nanostructure 96 has been shown. However, typicallythere is an array of nanostructures 96.

In some embodiments, the device is an LED. Each photo-active junctionmay be able to output light of a different range of wavelengths. Forexample, the first photo-active junction 703 may output blue light andthe second photo-active junction 705 may output green light. In someembodiments, there are three or more photo-active junctions. Therefore,the device may output three or more different colors.

FIG. 7A shows the control logic 725 activating the first photo-activejunction 703 and de-activating the second photo-active junction 705.FIG. 7B shows the control logic 725 activating the second photo-activejunction 705 and de-activating the first photo-active junction 703. FIG.7C shows the logic 725 controlling (e.g., activating/de-activating) thephoto-active junctions 703, 705 independently. Thus, the device 300might output blue light when the first photo-active junction 703 isactive and red light when the second photo-active junction 705 isactive.

The control logic 725 may be implemented with hardware, software, orsome combination of hardware and software. The software used may bestored on one or more processor readable storage devices including harddisk drives, CD-ROMs, DVDs, optical disks, floppy disks, tape drives,RAM, ROM, flash memory, or other suitable storage devices. The softwarecan be used to program one or more processors to perform the functionsof the control logic 725 described herein. In alternative embodiments,some or all of the control logic 725 can be implemented by dedicatedhardware including custom integrated circuits, gate arrays, FPGAs, PLDs,and special purpose computers.

FIG. 8A is a flowchart of one embodiment of a process 800 ofindependently controlling different photo-active junctions of anoptoelectronic device. Process 800 may be performed by the control logic725. In step 802, the control logic 725 controls first photo-activejunctions 703 to generate or detect light having a first range ofwavelengths. Note that each nanostructure 96 may have its ownphoto-active junctions. Therefore, process 800 will refer to controllingphoto-active “junctions” of different nanostructures 96. For example,the control logic 725 causes the first photo-active junctions 703 ofdifferent nanostructures 96 to output blue light. Alternatively, thecontrol logic 725 causes the first photo-active junctions 703 ofdifferent nanostructures to detect blue light. In step 804, the controllogic 725 independently controls second photo-active junctions 705 togenerate or detect light having a second range of wavelengths. Forexample, the control logic 725 causes the second photo-active junctions703 of different nanostructures 96 to output red light (or some othercolor). Alternatively, the control logic 725 causes the secondphoto-active junctions 705 of different nanostructures to detect redlight.

FIG. 8B is a flowchart of one embodiment of a process 815 ofindependently controlling different photo-active junctions of anoptoelectronic device. FIGS. 7A-7B will be referred to when discussingprocess 815. Process 815 provides more details of one embodiment ofprocess 800. In step 820, the control logic 725 applies voltages tosecond and third electrical contacts (e.g., contacts 104 c, 104 b) inorder to de-activate the second photo-active junctions 705. For example,the same magnitude voltage is applied to each contact 104 b, 104 c. Suchas strategy may de-activate a photo-active junction for an LED. Thejunction might also be reverse biased to de-activate for LED operation.Note that junctions of photo-detectors may be de-activated by breaking acircuit in which the diode junction resides. Therefore, one way ofactivating/de-activating photo-detector junctions is to reverse bias foractivation and open the circuit for de-activation.

In step 822, the control logic 725 applies voltages to first and secondelectrical contacts to activate the first photo-active junctions 703.For example, the control logic 725 applies a positive voltage to topsidewall electrical contact 104 c while grounding intermediate sidewallelectrical contact 104 a in order to forward bias the first photo-activejunctions 703 if the device of FIG. 7A is being used as an LED. If thedevice of FIG. 7A is being used as a photo-detector (or imaging device),the voltages may be reversed in order to reverse bias the firstphoto-active junctions 703. Note that detection of light may not requirethat the diode junction be biased. However, the previously mentionedcircuit should be closed such that current generated by the photo-activejunction may be detected. If the n-type regions 302 and p-type regions304 are switched the voltages applied to the contacts 104 a, 104 c maybe reversed for each case in order to activate the first junctions 703.If the n-type regions 302 and p-type regions 304 are switched thevoltages applied to the contacts 104 a, 104 c may be reversed for eachcase in order to activate the first junctions 703.

Step 822 may be performed concurrently with step 820. As one example,the control logic 725 applies the same voltage to the bottom sidewallelectrical contact 104 b as is applied to the intermediate sidewallelectrical contact 104 c. Therefore, no net voltage exists across thesecond photo-active junctions 705. However, a different voltage might beapplied to the bottom electrical contact 104 b in order to de-activateit. For example, for an LED the junction might be reversed biased tode-activate it. Alternatively, for an LED, the junction might be biasedwith small voltage that is not sufficient to generate much, if any,light. Together, steps 820 and 822 are one embodiment of step 802 ofprocess 800.

In step 824, the control logic 725 applies voltages to the firstelectrical contact (e.g., contact 104 a) and the second electricalcontact (e.g., contact 104 b) in order to de-activate the firstphoto-active junctions 703. For example, the same magnitude voltage isapplied to each contact 104 a, 104 b. Such as strategy may de-activate aphoto-active junction for an LED. The junction might also be reversebiased to de-activate for LED operation. Note that junctions ofphoto-detectors may be de-activated by breaking a circuit in which thediode junction resides. Therefore, one way of activating/de-activatingphoto-detector junctions is to reverse bias for activation and open thecircuit for de-activation.

In step 826, the control logic 725 applies voltages to the second andthird electrical contacts to activate the second photo-active junctions705. For example, the control logic 725 applies a positive voltage tointermediate sidewall electrical contact 104 c, while grounding thebottom sidewall electrical contact 104 b in order to forward bias thesecond photo-active junctions 705 if the device of FIG. 7B is being usedas an LED. If the device of FIG. 7B is being used as a photo-detector,the voltages may be reversed in order to reverse bias the secondphoto-active junctions 705. As mentioned, detection of light may notrequire that the diode junction be biased, but the circuit should beclosed. If the n-type regions 306 and p-type regions 304 are switched,then the voltages applied to the contacts 104 b, 104 c may be reversedfor each case in order to activate the second junctions 705. If then-type regions 306 and p-type regions 304 are switched, then thevoltages applied to the contacts 104 b, 104 c may be reversed for eachcase in order to activate the second junctions 705.

Step 826 may be performed concurrently with step 824. As one example,the control logic 725 applies the same voltage to the top sidewallelectrical contact 104 a as is applied to the intermediate sidewallelectrical contact 104 c. Therefore, no net voltage exists across thefirst photo-active junctions 703. However, a different voltage might beapplied to the top electrical contact 104 a in order to de-activate thefirst photo-active junctions 703. Together, steps 824 and 826 are oneembodiment of step 804 of process 800.

In one embodiment, independently controlling the photo-active junctionsincludes activating the junctions 703, 705 for different percentages oftime. Each junction 703, 705 may or may not be active at the same time.FIG. 8C is a flowchart of one embodiment of a process 840 ofindependently controlling different photo-active junctions of anoptoelectronic device. FIG. 7C will be referred to when discussingprocess 840. Process 840 provides more details of one embodiment ofprocess 800.

In step 842, the control logic 725 applies some voltage to theintermediate electrical contact 104 b. As an example, a voltage that issufficient to forward bias the junctions is applied, assuming the othercontacts are grounded.

In step 844, the control logic 725 controls the voltage to the topelectrical contact 104 a in order to activate the first photo-activejunctions 703 for some percentage of time. For example, the controllogic 725 grounds top electrical contact 104 a in order to forward biasthe first photo-active junctions 703 (assuming the device is being usedas an LED). The control logic 725 may de-activate the first photo-activejunctions 703 by applying Vbias to the top electrical contact 104 a suchthat there is no voltage across. Thus, by controlling the voltage to thetop electrical contact 104 a the percentage of time that the firstphoto-active junctions 703 are active can be controlled. Note that othersuitable voltages may be used if the device is being used as aphoto-detector or if the p-type and n-type regions are switched.Together, steps 842 and 844 are one embodiment of step 802 of process800.

In step 846, the control logic 725 controls the voltage to the bottomelectrical contact 104 b in order to activate the second photo-activejunctions 705 for some percentage of time. For example, the controllogic 725 grounds bottom electrical contact 104 b in order to forwardbias the second photo-active junctions 705 (assuming the device is beingused as an LED). The control logic 725 may de-activate the secondphoto-active junctions 705 by applying Vbias to the bottom electricalcontact 104 b such that there is no voltage across. Together, steps 842and 846 are one embodiment of step 802 of process 800.

Note that the control logic 725 is able to control each junction 703,705 by selecting the amount of time that each junction is active. Forexample, the control logic 725 could activate the first photo-activejunctions 703 for 50 percent of the time and the second photo-activejunctions 705 for 100 percent of the time. If the device is being usedas an LED, this may result in a brighter light intensity of the lightthat is generated by the second photo-active junctions 705 than thelight that is generated by the first photo-active junctions 703.

Another option for independently controlling the junctions 703, 705 isto vary the magnitude of the voltages across the junctions 703, 705. Forexample, a large voltage may be applied to the first photo-activejunctions 703 to heavily forward bias the first junctions 703. On theother hand a relatively small voltage may be applied to the secondphoto-active junctions 705 to weakly forward bias the second junctions705. The control logic 725 may accomplish this by selecting themagnitude of the voltage applied to the top 104 a and bottom 104 bcontacts, respectively.

FIG. 9 depicts one embodiment of a process 900 of fabricating anoptoelectronic device. Process 900 may be used to form a device such asdevices depicted in FIGS. 3A, 3B, 7A, 7B, and 7C. In step 902,nanostructures are formed. Step 902 may be similar to step 502 ofprocess 500 and will not be discussed in detail. In step 904, a bottomelectrical contact 104 b is formed. Step 904 may be similar to step 504of process 500 and will not be discussed in detail. In one embodiment,the bottom electrical contact is not a sidewall electrical contact. Forexample, the bottom electrical contact could be located below thesubstrate or between the substrate and the nanostructures 96.

In step 906, an intermediate sidewall electrical contact 104 b isformed. Step 906 may include depositing an insulator over the bottomelectrical contact 104 b, etching back the insulator to a desired level,depositing a metal over the insulator, and etching back the metal.

In step 908, a top electrical contact is formed. In one embodiment, thetop electrical contact is a top sidewall electrical contact 104 a. Aprocess similar to the ones in either FIG. 5B or 5C might be used toform a top sidewall electrical contact 104 a. In one embodiment, the topelectrical contact is not a sidewall contact.

In step 910, edges of the electrical contacts are exposed. The edges maybe exposed using a wide variety of techniques including etching andphotolithography. In step 912 leads are attached to the electricalcontacts. FIG. 3C depicts an example of a device 300 having exposededges with leads 112 attached.

In step 914, control logic 725 is provided. Step 725 may include formingswitches to connect the contacts 104 to different voltage sources, andproviding hardware or software to control the switches. Switches may beimplemented by transistors, logic gates, etc. The control logic 725 maybe operable to perform functions such as those discussed in connectionwith FIGS. 7A-7C and 8A-8C. The control logic 725 may include anycombination of hardware and/or software.

Pixilated Device

One embodiment includes a pixilated nanostructure optoelectronic device.Different groups of one or more nanostructures 96 may be controlledseparately as individual pixels. Each pixel may have multiplephoto-active junctions. Each junction may be capable of generating ordetecting light of a different range of wavelengths. For example, onejunction may be capable of blue light generation, another red light, andstill another green light. The different photo-active junctions in eachnanostructure 96 may be independently controlled.

FIG. 10A depicts one embodiment of a pixilated nanostructureoptoelectronic device 1000. Only a small portion of the device 1000 isdepicted. The device 1000 includes a first layer of p-contacts 1012 thatrun in the y-direction, a first layer of n-contacts 1014 that run in thex-direction, a second layer of p-contacts 1016 that run in they-direction, and a second layer of n-contacts 1018 the run in thex-direction. Each contact may be a long strip of metal, for example.Insulation 1025 between layers of contacts is depicted in FIG. 10A.

Note that the p-contacts 1012 may be one embodiment of top sidewallelectrical contacts. Note that tops 96 a of the nanostructures 96 areexposed to allow light to enter or leave the nanostructures 96 from thetops 96 a without passing through the p-contacts 1012. In this case, thespaces between the nanostructures 96 are not completely filled by thetop sidewall electrical contacts. The region between contacts at a givenlayer may be filled with insulation; however, this insulation is notdepicted in FIG. 10A so as to not obscure the diagram. Therefore, insome embodiments, the combination of the top sidewall contacts andinsulation completely fills the spaces between the nanostructures at alevel near the tops of the nanostructures 96. In some embodiments, thetop contacts are not sidewall contacts.

Each contact may have a contact pad 1032 at the end to which anelectrical lead 112 is attached. Therefore, the control logic 725 mayapply a separate voltage (or provide a current) to each contact. In somecases, a contact may be electrically isolated from the voltage sourcesuch that the contact is floated. Only some of the electricalconnections between the control logic 725 and the electrical leads 112are explicitly depicted so as to not obscure the diagram.

A sub-pixel corresponds to the intersection of certain p-contacts andn-contacts. For example, a blue sub-pixel may correspond to theintersection of one of the p-contacts 1012 in the first layer ofp-contacts 1012 and one of the n-contacts 1014 in the first layer ofn-contacts 1014. As another example, a green sub-pixel may correspond tothe intersection of one of the n-contacts 1014 in the first layer ofn-contacts 1014 and one of the p-contacts 1016 in the second layer ofp-contacts 1016. As a further example, a red sub-pixel may correspond tothe intersection of one of the p-contacts 1016 in the second layer ofp-contacts 1016 and one of the n-contacts 1018 in the second layer ofn-contacts 1018. Note that the p-contacts may be switched withn-contacts.

FIG. 10B depicts a side cross sectional perspective of a portion of thedevice 1000 of FIG. 10A. FIG. 10B shows a single nanostructure 96 andtwo p-contacts 1012, 1016, as well as two n-contacts 1014, 1018 that arephysically and electrically connected to the nanostructure sidewall.Note that a given contact may surround the nanostructure 96. FIG. 10Balso depicts control logic 725 that controls switches or other logic inorder to bias the photo junctions appropriately to activate each photojunction separately.

The p-n junction of p-type region 1002 and n-type region 1004 may have afirst band gap energy. The p-n junction of p-type region 1006 and n-typeregion 1004 may have a second band gap energy. The p-n junction ofp-type region 1006 and n-type region 1008 may have a third band gapenergy. Appropriate selection of the materials may be used such that ablue sub-pixel, a green sub-pixel and a red sub-pixel may be formed froma group of one or more nanostructures 96.

Returning again to FIG. 10A, at the junction of a given p-contact 1012and a given n-contact 1014 there is a single nanostructure depicted(note that the single nanostructure is also the junction of one of thep-contacts 1016 and one of the n-contacts 1018). However, there may be agroup of one or more nanostructures at the contact junction. Herein, theterm “nanostructure group” will be used to refer to a group of one ormore nanostructures that are being controlled by the same set of thep-contacts and n-contacts. For example, referring to FIG. 10A, each ofthe depicted nanostructures 96 is being controlled by its own set ofp-contacts and n-contacts. For some embodiments, a pixel may be definedas including a blue sub-pixel, a red sub-pixel and a green sub-pixel.Therefore, a nanostructure group may function as a pixel.

FIG. 10C depicts one embodiment of a biasing scheme for a pixilateddevice 1000 such as the example devices depicted in FIGS. 10A and 10B.The diagram shows three p-contacts running in the y-direction and threen-contacts running in the x-direction. For example, the contacts couldbe p-contacts 1012 and n-contacts 1014 from FIG. 10A. As anotherexample, the contacts could be p-contacts 1016 and n-contacts 1018 fromFIG. 10A. As still another example, the contacts could be n-contacts1014 and p-contacts 1016 from FIG. 10A. Thus, the contacts may be onadjacent contact layers of the device 1000 of FIG. 10A. It will beunderstood that the p-contacts and n-contacts are not physicallytouching. Each diode represents one sub-pixel 1050. Each diodecorresponds to a p-type region and an n-type region of a nanostructuregroup. Note that the diode could be a p-i-n diode.

Example bias voltages are shown applied to the contacts for LEDoperation. One of the sub-pixels (in the center) is selected and theothers are un-selected. By selected it is meant that the photo-activeregion is activated by the applied voltages. For example, for an LED thesub-pixels may be biased to emit light.

Specifically, the selected sub-pixel 1050 has the voltage Vhigh appliedto its p-contact and Vlow is applied to its n-contact. As one example,Vhigh-Vlow is sufficient to forward bias the diode for LED operation. Asone example, Vlow may be a 0 Volts and Vhigh may be a voltage that isabove the turn on voltage of the diode. However, Vlow is not required tobe 0 Volts. Rather, Vlow could be greater or less than 0 Volts.Therefore, Vhigh is not necessarily a voltage that is above the turn onvoltage of the diode.

Some of the unselected sub-pixels will have Vhigh-Vhigh across theirdiodes. Other sub-pixels have Vlow-Vlow across their diodes. Therefore,no net voltage appears across those diode junctions such that thesub-pixels are off. Some of the unselected sub-pixels will haveVlow-Vhigh across their diodes. The voltage Vlow-Vhigh should be onethat does not activate the sub-pixels. For example, Vlow-Vhigh mightreverse bias the diode such that the sub-pixel is off.

Note that more than one sub-pixel in a given layer may be selected atthe same time by applying appropriate select voltages to the appropriatep-contact and n-contacts. For example, any number of blue sub-pixels maybe selected at the same time. As another example, any number of redsub-pixels may be selected at the same time. In some embodiments, whenthe blue sub-pixels are being controlled, the red and green sub-pixelsare dormant. For example, when the blue sub-pixels are being selected orunselected using a bias scheme such as depicted in FIG. 10C, all of thered and green sub-pixels are temporarily off. Note that FIG. 10C onlyshows contacts for two different levels. However, in some embodiments,there are four levels of contacts (see, for example, FIG. 10A). In someembodiments, the other contacts are floated when Vhigh and Vlow areapplied to the contacts in FIG. 10C in order to keep the othersub-pixels off. However, other techniques may be used to keep the othersub-pixels off.

The foregoing biasing scheme of FIG. 10C is just one example. Otherbiasing schemes may be used. Modifications to the biasing scheme can bemade for the case in which the diode is facing the opposite direction.

FIG. 10D shows one example biasing scheme for photo-detector operationfor a pixilated device 1000 such as the example devices depicted inFIGS. 10A and 10B. The diagram shows three p-contacts running in they-direction and three n-contacts running in the x-direction. Forexample, the contacts could be p-contacts 1012 and n-contacts 1014 fromFIG. 10A. As another example, the contacts could be p-contacts 1016 andn-contacts 1018 from FIG. 10A. As still another example, the contactscould be n-contacts 1014 and p-contacts 1016 from FIG. 10A. Thus, thecontacts may be on adjacent contact layers of the device 1000 of FIG.10A. It will be understood that the p-contacts and n-contacts are notphysically touching. Each diode represents one sub-pixel 1050. Eachdiode corresponds to a p-type region and an n-type region of ananostructure group. Note that the diode could be a p-i-n diode.

Example bias voltages are shown applied to the contacts forphoto-detector operation. One of the sub-pixels (in the center) isselected and the others are un-selected. By selected it is meant thatthe photo-active region is activated by the applied voltages. For aphoto-detector, the sub-pixel may be reversed biased to detect light.However, note that the junction could be un-biased also. The amount ofcurrent that is generated by the selected sub-pixel is detected by thecircuit. For example, an ammeter (A) detects the current. Leaving thecircuit open is one way to de-select a sub-pixel. Note that no voltagesneed to be applied to some of the n-contacts and p-contact, as certainsub-pixels are not selected.

Specifically, the selected sub-pixel 1075 has the voltage Vhigh appliedto its re-contact and Vlow is applied to its p-contact. As alreadymentioned, it may not be necessary to apply voltages so long as thecircuit is closed. However, reverse biasing the junction may improveoperation. Some of the unselected sub-pixels will have a voltage appliedto one contact. However, the other contact may be floated (e.g., thecircuit may be open at the other contact). Therefore, the junction willnot be active.

Note that additional sub-pixels could be selected for photo-detectoroperation by reverse biasing diode junctions similar to how the selectedsub-pixel 1075 is selected. For example, suitable Vhigh and Vlowvoltages may be applied to other n-contacts and p-contacts.

In some embodiments, at least two of the three colors of sub-pixels areselected (e.g., “on” or “active”) at the same time. For example, both ared and a blue sub-pixel in the same nanostructure group may be selectedat the same time. As another example, a red sub-pixel is selected in onenanostructure group while a blue sub-pixel is selected in anothernanostructure group.

In some embodiments, any color sub-pixel may be selected at one point intime. For example, all sub-pixels in the same nanostructure group may beselected at the same time. As another example, some nanostructure groupshave their blue sub-pixel selected at the same time that othernanostructure groups have their red sub-pixel selected and at the sametime that other nanostructure groups have their green sub-pixelselected. Many other combinations are possible.

FIG. 11 depicts a flowchart of embodiment of a process 1100 of operatingan optoelectronic device. The process 1100 may be used to operate adevice 1000 such as the one depicted in FIG. 10A or 10B; however, theprocess is not limited to those devices. For example, the process couldbe used to operate a three color LED display. The process 1100 mightalso be used to operate a photo-detector, imaging device, orspectrometer. The optoelectronic device may include a nanostructurearray with groups of one or more nanostructures in the array(“nanostructure groups”) forming pixels having at least two sub-pixels.

In step 1102, first sub-pixels (e.g., blue sub-pixels) are controlled togenerate or detect light of a first range of wavelengths. For example,the control logic 725 applies appropriate Vhigh and Vlow voltages top-contacts 1012 and n-contacts 1014 that are associated with the bluesub-pixels. Examples of LED and photo-detector operation were describedabove. Other examples are described below. In one embodiment, the othersub-pixels are off when the blue sub-pixels are being controlled. Onetechnique for keeping the other sub-pixels off is to float the othercontacts. For example, p-contacts 1016 and n-contacts 1018 may befloated when Vhigh and Vlow are applied to the p-contacts 1012 andn-contacts 1014. However, other techniques can be used to keep the redand green sub-pixels off when controlling the blue sub-pixels.

In step 1104, second sub-pixels (e.g., green sub-pixels) are controlledto generate or detect light of a second range of wavelengths. Forexample, the control logic 725 applies appropriate Vhigh and Vlowvoltages to n-contacts 1014 and p-contacts 1016 that are associated withthe green sub-pixels. In one embodiment, the other sub-pixels are offwhen the green sub-pixels are being controlled. For example, p-contacts1012 and n-contacts 1018 may be floated when Vhigh and Vlow are appliedto the p-contacts 1014 and p-contacts 1016. However, other techniquescan be used to keep the red and blue sub-pixels off when controlling thegreen sub-pixels.

In step 1106, third sub-pixels (e.g., red sub-pixels) are controlled togenerate or detect light of a third range of wavelengths. For example,the control logic 725 applies appropriate Vhigh and Vlow voltages top-contacts 1016 and n-contacts 1018 that are associated with the redsub-pixels. In one embodiment, the other sub-pixels are off when the redsub-pixels are being controlled. For example, p-contacts 1012 andn-contacts 1014 may be floated when Vhigh and Vlow are applied to thep-contacts 1016 and n-contacts 1018. However, other techniques can beused to keep the green and blue sub-pixels off when controlling the redsub-pixels.

Note that the first, second, and third ranges of wavelengths aredifferent ranges. However, there may or may not be overlap in theranges. For example, one sub-pixel may be configured to absorb/emitphotons from A nm to B nm, another sub-pixel may be configured toabsorb/emit photons from B nm to C nm, another sub-pixel may beconfigured to absorb/emit photons from C nm to D nm. As another example,one sub-pixel may be configured to absorb/emit photons from A nm to Bnm, another may be configured to absorb/emit photons from B+x nm to Cnm, another may be configured to absorb/emit photons from C+y nm to D nm(where x and y are positive values). As still another example, onesub-pixel may be configured to absorb/emit photons from A nm to B nm,another may be configured to absorb/emit photons from B−x nm to C nm,another may be configured to absorb/emit photons from C−y nm to D nm.Other variations are possible; the foregoing are intended as examples.

Note also that two or more of steps 1102, 1104, and 1106 may beperformed simultaneously. In some embodiments, different colors ofsub-pixels may be controlled at the same time. Therefore, a redsub-pixel could be selected at the same time that a blue sub-pixel isselected, for example. Further details of selecting different colors ofsub-pixels at the same time are discussed below.

Using the process 1100 of FIG. 11, essentially any color of light may begenerated. For example, white light could be generated by activatingselected blue sub-pixels for a period of time (while green and redsub-pixels are off), activating selected green sub-pixels for a periodof time (while green and blue sub-pixels are off), and activatingselected red sub-pixels for a period of time (while green and bluesub-pixels are off). However, in some embodiments, two or more colors ofsub-pixels are selected at the same time. For example, white light couldbe generated by selecting a blue sub-pixel, a green sub-pixel, and a redsub-pixel at the same time. Note that the blue, green and red sub-pixelsmay be in the same nanostructure group. Further details of such atechnique are discussed below.

Another option for generating different colors is to select differentcolor sub-pixels from adjacent nanostructure groups. As mentioned,because a nanostructure group of some embodiments has three colors ofsub-pixels, a nanostructure group may be considered to be a pixel.However, another option for forming a “pixel” is to use three adjacentnanostructure groups. For example, a pixel could comprise the bluesub-pixel from one nanostructure group, the green sub-pixel from anadjacent nanostructure group, and the red sub-pixel from anotheradjacent nanostructure group. Thus, as one example, white light could beformed by selecting a blue, red and green sub-pixel from adjacentnanostructure groups at the same time.

Example Biasing Schemes for Operating Different Color Sub-PixelsSimultaneously

FIGS. 12A-12C depict one embodiment of a biasing scheme in whichdifferent colors of sub-pixels are controlled simultaneously. Thisscheme may be used for LED operation, for example. This allows differentcolor of sub-pixels to be selected at the same time. In this embodiment,two sub-pixels in the same nanostructure group may be controlledsimultaneously. For example, the red sub-pixels and the green sub-pixelsmay be controlled (or operated) at the same time. For example, a redsub-pixel and a green sub-pixel in the same nanostructure group may beselected at the same time. As another example, a red sub-pixel in onenanostructure group may be selected and at the same time that a greensub-pixel in another nanostructure group is selected. In someembodiments, steps 1102, 1104, and 1106 of FIG. 11 are performed usingthe biasing scheme depicted in FIGS. 12A-12C.

FIGS. 12A-12C depict three different levels of contacts. One set ofp-contacts 1202 that run in the y-direction are shown as solid lines todepict they are at one level. A second set of p-contacts 1204 that runin the y-direction are shown as dashed lines to depict they are atanother level. Also depicted as a set of n-contacts 1206 that run on thex-direction. The n-contacts are at a different level than thep-contacts. The three levels of contacts may correspond to three of thefour levels of contacts from the device 1000 of FIG. 10A. One set ofdiodes is depicted as being connected between p-contacts 1202 andn-contacts 1206. Those diodes represent one color of sub-pixels. Anotherset of diodes is depicted as being connected between p-contacts 1204 andn-contacts 1206. Those diodes represent another color of sub-pixels.

In FIG. 12A, one sub-pixel of each color is circled to indicate thatthey are selected sub-pixels 1210. All of the other sub-pixels are off(not selected) in this example. The example voltages that are applied tothe contacts are as follows. The voltage Vhigh is applied to theselected p-contact 1202, 1204 of each of the selected sub-pixels, whileVlow is applied to the selected n-contact 1206. Therefore, the diodejunctions are forward biased to select the sub-pixel. Note that thispertains to operation as an LED, for example. All other diodes areeither reverse biased or have no voltage applied across the diode.Therefore, the other sub-pixels are off (not selected).

In FIG. 12B, one sub-pixel is circled to indicate that it is theselected sub-pixel 1210. The example voltages that are applied to thecontacts are as follows. The voltage Vhigh is applied to the selectedp-contact 1202 of the selected sub-pixel, while Vlow is applied to theselected n-contact 1206. Therefore, the diode junction is forward biasedto select the sub-pixel. The p-contact 1204 for the other colorsub-pixel has Vlow applied such that its diode is un-biased. All otherdiodes are either reverse biased or have no voltage applied across thediode. Therefore, the other sub-pixels are off (not selected).

In FIG. 12C, one sub-pixel is circled to indicate that it is theselected sub-pixel 1210. The example voltages that are applied to thecontacts are as follows. The voltage Vhigh is applied to the selectedp-contact 1204 of the selected sub-pixel, while Vlow is applied to theselected n-contact 1206. Therefore, the diode junction is forward biasedto select the sub-pixel. The p-contact 1202 for the other colorsub-pixel has Vlow applied such that its diode is un-biased. All otherdiodes are either reverse biased or have no voltage applied across thediode. Therefore, the other sub-pixels are off (not selected).

In one embodiment, while the two colors of sub-pixels in FIGS. 12A-12Care being controlled (e.g., being selected or unselected), thesub-pixels for the other color is kept off. Then, while the two colorsof sub-pixels in FIGS. 12A-12C are off, the sub-pixels for the othercolor are being controlled (e.g., being selected or unselected). Forexample, 50 percent of the time red and green sub-pixels are beingcontrolled using the biasing scheme of FIGS. 12A-12C with bluesub-pixels off. The other 50 percent of the time blue sub-pixels arebeing controlled using the biasing scheme of FIG. 10C with red and greensub-pixels off.

Note that two different colors of sub-pixels may be simultaneouslyselected when operating as a photo-detector. FIG. 12D shows one possiblebiasing scheme for selecting two different colors of sub-pixels in thesame nanostructure for photo-detector operation. As can be seen twosub-pixels are reversed biased and therefore, selected forphoto-detector operation. Un-selected sub-pixels have open circuits, anddo not require a voltage applied to each contact. As mentioned,operation may be possible without basing the contacts, so long as thecircuit is closed. Also note that one color sub-pixel can be selected inone nanostructure, while selecting another color sub-pixel in anothernanostructure. For example, a red (but not green) sub-pixel could beselected in one nanostructure while selecting a green (but not red)sub-pixel in the other nanostructure.

FIGS. 13A-13H depict one embodiment of a biasing scheme in which threedifferent color sub-pixels are operated or controlled simultaneously.The scheme may be used for LED operation, for example. In thisembodiment, three sub-pixels in the same nanostructure group may becontrolled simultaneously. For example, any combination of a bluesub-pixel, a red sub-pixel and a green sub-pixel in the samenanostructure group may be selected at the same time. Also note that adifferent nanostructure group may have a different combination ofsub-pixels selected at the same time. For example, one nanostructuregroup may have its blue and green sub-pixels selected at the same timethat another nanostructure group has its red and blue sub-pixelsselected. In some embodiments, steps 1102, 1104, and 1106 of FIG. 11 areperformed using the biasing scheme depicted in FIGS. 13A-13H.

FIGS. 13A-13H depict four different levels of contacts. These maycorrespond to the contacts in FIG. 10A. One set of p-contacts 1012 thatrun in the y-direction are shown as solid lines to depict they are atone level. A second set of p-contacts 1016 that run in the y-directionare shown as dashed lines to depict they are at another level. Alsodepicted as two sets of n-contacts 1014, 1018 that run in thex-direction.

One set of diodes is depicted as being connected between p-contacts 1012and n-contacts 1014. Those diodes represent one color of sub-pixels(e.g., blue sub-pixels). Another set of diodes is depicted as beingconnected between p-contacts 1016 and n-contacts 1014. Those diodesrepresent another color of sub-pixels (e.g., green sub-pixels). Stillanother set of diodes, which represent a third color of sub-pixels(e.g., red sub-pixels), is depicted as being connected betweenp-contacts 1016 and n-contacts 1018.

FIGS. 13A-13H show voltages that may be applied to the contacts in orderto selectively operate different combinations of sub-pixels in thecenter pixel 1310. All other sub-pixels are off on each of FIGS.13A-13H. However, note that the other sub-pixels could be on if suitablevoltages were applied to their contacts. In this example, the voltageVhigh may be a turn on voltage of a diode. The voltage Vlow may be−Vhigh. In general, forward biasing the diode may be used to select thesub-pixel. Diodes that are either un-biased or reverse biased result inoff sub-pixels. The foregoing assumes operation as an LED.

In FIG. 13A all sub-pixels are off due to grounding all contacts. Notethat even the circled sub-pixels are off in FIG. 13A; however, they arecircled to highlight that those three sub-pixels form the pixel thatthis discussion is focused upon. In FIG. 13B, the blue (circled)sub-pixel is on, whereas the green and red sub-pixels are off. In FIG.13C, the green (circled) sub-pixel is on, whereas the blue and redsub-pixels are off. In FIG. 13D, the red sub-pixel (circled) is on,whereas the green and red sub-pixels are off. In FIG. 13E, the green andblue sub-pixels are on, whereas the red sub-pixel is off. In FIG. 13F,the green and red sub-pixels (circled) are on, whereas the bluesub-pixel is off. In FIG. 13G, the red and blue sub-pixels are on,whereas the green sub-pixel is off. Note that this is the only case inwhich the voltage Vlow is used. For example, the red sub-pixel is biasedby the applying GND to one terminal and Vlow to the other terminal toforward bias the diode. In FIG. 13H, the red, blue and green sub-pixels(circled) of the pixel under discussion are all on.

Note that three different colors of sub-pixels may be simultaneouslyselected when operating as a photo-detector. For example, FIG. 13I showsone possible biasing scheme for selecting three different colors ofsub-pixels in the same nanostructure for photo-detector operation. Ascan be seen three sub-pixels are reversed biased and therefore, selectedfor photo-detector operation. Circuits for detecting the generatedcurrents are not explicitly shown in FIG. 13I. Un-selected sub-pixelshave open circuits, and do not require a voltage applied to both oftheir contacts. As mentioned, operation may be possible without basingthe contacts, so long as the circuit is closed. Also note that anycombination of colors of sub-pixels can be selected in onenanostructure, while selecting a different combination of colors ofsub-pixels in another nanostructure. For example, a red and a blue (butnot green) sub-pixel could be selected in one nanostructure whileselecting a green and red (but not blue) sub-pixel in the othernanostructure.

Example Process of Fabricating a Pixilated Optoelectronic Device

FIG. 14 depicts one embodiment of a process 1400 of fabricating anoptoelectronic device. Process 1400 may be used to form a device such asdevices 1000 depicted in FIGS. 10A and 10B. Reference will be made tothose devices, but process 1400 is not so limited. In step 1402,nanostructures are formed. Step 1402 may be similar to step 502 ofprocess 500 and will not be discussed in detail. In step 1404, a row ofelectrical contacts that run in a first direction is formed. Step 1404may be performed by depositing metal, then patterning and etching toform rows of contacts. As one example, n-contacts 1018 are formed. Notethat this row could be p-contacts, depending on the doping of thenanostructures 96.

In step 1406 insulation is formed. For example, SOG, silicon dioxide,photoresist or another material is deposited. The insulation may fillspaces between the rows of contacts and also may form a layer over therows to serve as a base for the next row of contacts.

In step 1408, a row of electrical contacts that run in a seconddirection is formed. The second direction may be orthogonal to thefirst. Step 1408 may be performed by depositing metal, then patterningand etching to form rows of contacts. As one example, p-contacts 1016are formed. In step 1410, additional insulation is formed. For example,SOG, silicon dioxide, photoresist or another material is deposited. Theinsulation may fill spaces between the rows of contacts 1016 and alsomay form a layer over the rows of contacts 1016 to serve as a base forthe next row of contacts.

In step 1412, another row of electrical contacts that run in the firstdirection is formed. Step 1412 may be performed by depositing metal,then patterning and etching to form rows of contacts. As one example,n-contacts 1014 are formed. In step 1414, additional insulation isformed. For example, SOG, silicon dioxide, photoresist or anothermaterial is deposited. The insulation may fill spaces between the rowsof contacts 1014 and also may form a layer over the rows of contacts1014 to serve as a base for the next row of contacts.

In step 1416, another row of electrical contacts that run in the seconddirection is formed. Step 1416 may be performed by depositing metal,then patterning and etching to form rows of contacts. As one example,p-contacts 1012 are formed. In step 1418, additional insulation isformed (optional). For example, SOG, silicon dioxide, photoresist oranother material is deposited. The insulation may fill spaces betweenthe rows of contacts 1012.

In step 910, edges of the electrical contacts are exposed. The edges maybe exposed using a wide variety of techniques including etching andphotolithography. In step 912 leads are attached to the electricalcontacts. FIG. 10A depicts an example of a device 1000 having exposededges with leads 112 attached.

In step 914, control logic 725 is provided. Step 725 may include formingswitches to connect the contacts 104 to different voltage sources, andproviding hardware or software to control the switches. The controllogic 725 may be operable to perform functions such as those discussedin connection with FIGS. 7A-7C, 8A-8C and 11. The control logic 725 mayinclude any combination of hardware and/or software.

Other Variations of Pixilated Nanostructure Optoelectronic Devices

FIG. 15A is a diagram of one embodiment of a pixilated nanostructureoptoelectronic device. The device is similar to the one depicted in FIG.10A. However, it has an additional set of p-contacts 1015 that run inthe y-direction. There is also an additional layer of insulation 1025,which is located between the p-contacts 1015 and p-contacts 1016.

FIG. 15B is a side cross-sectional view of the device 1500 of FIG. 15A.This view shows how the contacts and insulation make connection to oneof the nanostructures 96. Note that the p-type semiconductor 1006 isseparated into two regions 1006 a, 1006 b by a layer of insulation 1525.This may aid is allowing the red sub-pixel to be operated independent ofthe green sub-pixel. The insulation 1525 may be an insulatingsemiconductor that is formed during growth of the nanostructures 96.Therefore, the nanostructures 96 have a region having alternating layersof a semiconductor having a first type of conductivity (e.g., region1006 a), an insulator (e.g., 1525), and a semiconductor having the firsttype of conductivity (e.g., 1006 b).

In this example, the n-contacts 1014 and 1018 are connected to ground.The control logic 725 connects p-contact 1012 to Vhigh to select theblue sub-pixel. The control logic 725 connects p-contact 1015 to Vhighto select the green sub-pixel. The control logic 725 connects p-contact1016 to Vhigh to select the red sub-pixel. In one embodiment, thecontrol logic 725 connects the p-contact 1012 to GND to unselect (turnoff) the blue sub-pixel. In one embodiment, the control logic 725connects the p-contact 1015 to GND to unselect (turn off) the greensub-pixel. In one embodiment, the control logic 725 connects thep-contact 1016 to GND to unselect (turn off) the red sub-pixel.Therefore, the control logic 725 is able to independently select any ofthe sub-pixels. Note that a different biasing scheme may be used toselect the sub-pixels.

Note that alternatives to the structure of FIGS. 15A and 15B is to havethe extra layer of insulation separate the blue and green sub-pixelsinstead of (or in addition to) the insulation 1025 that separates thered and green sub-pixels. For example, n-type semiconductor 1004 couldbe separated into two regions by an insulator. In such an embodiment,the n-contact 1014 could be replaced by two contacts separated by aninsulator.

Note that numerous examples have been provided in which the devices havethree colors of sub-pixels. However, the device may have any number ofsub-pixels. These sub-pixels may correspond to many differentwavelengths of light. It is not required that a sub-pixel corresponds toa wavelength of visible light.

In some embodiment, an optoelectronic device with sidewall electricalcontacts may be operated as a spectrometer. For example, additionallayers may be added to the device 1000 of FIGS. 10A-10B or the device300 of FIGS. 3A-3C to allow for detection of light at many more distinctwavelength ranges. The control logic 725 may be configured to separatelycontrol each layer to detect light of each distinct wavelength range.Note that there may be some overlap in the range of wavelengths that twodifferent sub-pixels correspond to.

Example Computing Platform

In various embodiments, the control logic 725 executes computer readableinstructions that are stored on computer readable media. For example,process 800, 815, 840, and 1100 may be implemented at least in part byexecuting, on a processor, instructions that are stored on a computerreadable storage medium. Computer readable media can be any availablemedia that can be accessed by the electronic devices. By way of example,and not limitation, computer readable media may comprise computerstorage media. Computer storage media includes volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich can be used to store the computer readable instructions and whichcan accessed by the electronic devices.

The computer executable instructions may include program modules.Generally, program modules include routines, programs, objects,components, data structures, etc., that perform particular tasks orimplement particular abstract data types. Embodiments may also bepracticed in distributed computing environments where tasks areperformed by remote processing devices that are linked through acommunication network. In a distributed computing environment, programmodules may be located in both local and remote computer storage mediaincluding memory storage devices.

FIG. 16 is a block diagram of one embodiment of a computing system foruse with the present technology. Note that some embodiments do notrequire all of the elements depicted in FIG. 16. In some embodiments,the output display/photo-detector 1666 is an LED display. For example,technology described herein may be used to form pixels of the LED. Thecomputing device is able to implement the control logic 725 in order tocontrol the LED. In some embodiments, at least some of the functionalityof the control logic 725 is implemented by executing instructions on theprocessor 1650. In some embodiments, the output display/photo-detector1666 is able to function as a photo-detector. For example, technologydescribed herein may be used to form pixels of a photo-detector.

The computer system includes one or more processors 1650 and main memory1652 which stores, in part, instructions and data for execution byprocessor unit 1650. If the system of the present invention is wholly orpartially implemented in software, main memory 1652 can store theexecutable code when in operation. Also provided are a mass storagedevice 1654, peripheral device(s) 1656, user input device(s) 1660,output devices 1658, portable storage medium drive(s) 1662, a graphicssubsystem 1664 and an output display 1666. For simplicity, thecomponents are depicted as being connected via a single bus 1668.However, the components may be connected through one or more datatransport means. For example, processor unit 1650 and main memory 1652may be connected via a local microprocessor bus, and the mass storagedevice 1654, peripheral device(s) 1656, portable storage medium drive(s)1662, and graphics subsystem 1664 may be connected via one or moreinput/output (I/O) buses. Mass storage device 1654, which may beimplemented with a magnetic disk drive or an optical disk drive, is anon-volatile storage device for storing data and instructions for use byprocessor unit 1650. In one embodiment, mass storage device 1654 storesthe system software for implementing the present invention for purposesof loading to main memory 1652.

Portable storage medium drive 1662 operates with a portable non-volatilestorage medium, such as a floppy disk, to input and output data and codeto and from the computer system. In one embodiment, the system softwarefor implementing the embodiments is stored on such a portable medium,and is input to the computer system via the portable storage mediumdrive 1662. Peripheral device(s) 1656 may include any type of computersupport device, such as an input/output (I/O) interface, to addadditional functionality to the computer system. For example, peripheraldevice(s) 1656 may include a network interface for connecting thecomputer system to a network, a modem, a router, etc.

User input device(s) 1660 provides a portion of a user interface. Userinput device(s) 1660 may include an alpha-numeric keypad for inputtingalpha-numeric and other information, or a pointing device, such as amouse, a trackball, stylus, or cursor direction keys. In order todisplay textual and graphical information, the computer system includesgraphics subsystem 1664 and output display 1666. Graphics subsystem 1664receives textual and graphical information, and processes theinformation for output to output display 1666. Additionally, thecomputer system includes output devices 1658. Examples of suitableoutput devices include speakers, printers, network interfaces, monitors,etc.

The components contained in the computer system are those typicallyfound in computer systems suitable for use with the embodiments, and areintended to represent a broad category of such computer components thatare well known in the art. Thus, the computer system can be a personalcomputer, hand held computing device, telephone, mobile computingdevice, workstation, server, minicomputer, mainframe computer, or anyother computing device. The computer system can also include differentbus configurations, networked platforms, multi-processor platforms, etc.Various operating systems can be used including Unix, Linux, Windows,Macintosh OS, Palm OS, and other suitable operating systems.

One embodiment disclosed herein includes an optoelectronic devicecomprising a plurality of nanostructures that include photo-activeregions. The nanostructures have tops, bottoms, and sidewalls. Thedevice has a bottom electrical contact in electrical contact with thebottoms of the plurality of nanostructures, and a top electrical contactin electrical and physical contact with sidewalls of the plurality ofnanostructures, wherein the top electrical contact leaves a top portionof the plurality of nanostructures exposed to allow light to enter orleave the plurality of nanostructures from the tops of the plurality ofnanostructures without passing through the top electrical contact.

One embodiment disclosed herein includes a method for forming anoptoelectronic device comprising: forming a plurality of nanostructures,the nanostructures including photo-active regions, the plurality ofnanostructures having tops, bottoms, and sidewalls; forming a bottomelectrical contact in electrical contact with the bottoms of theplurality of nanostructures; and forming a top electrical contact inelectrical and physical contact with sidewalls of the plurality ofnanostructures, wherein the top electrical contact leaves a top portionof the plurality of nanostructures exposed to allow light to enter orleave the plurality of nanostructures from the tops of the plurality ofnanostructures without passing through the top electrical contact.

One embodiment disclosed herein includes an optoelectronic devicecomprising an array of nanostructures formed from a material thatincludes one more semiconductors, the nanostructures including one ormore p-n junctions, the nanostructures including photo-active regionsassociated with the p-n junctions, the plurality of nanostructureshaving tops, bottoms, and sidewalls, the nanostructures have spacesbetween them; a bottom electrical contact in electrical contact with thebottoms of the nanostructures; and a top electrical contact inelectrical and physical contact with the sidewalls of thenanostructures, wherein the top electrical contact is substantiallyopaque to light having a wavelength that is absorbed or generated by thephoto-active regions.

One embodiment disclosed herein includes a multi junction solar cellcomprising a plurality of nanostructures, the plurality ofnanostructures having first regions of a first conductivity type andsecond regions of a second conductivity type to form first p-njunctions, the plurality of nanostructures having third regions of thefirst conductivity type and fourth regions of the second conductivitytype to form second p-n junctions; and a bi-layer electricalinterconnect having a first material in electrical and physical contactwith the second regions and a second material in electrical and physicalcontact with the third regions, the first material and the secondmaterial are in electrical contact with each other to allow charge toflow between the second regions and the third regions through thebi-layer electrical interconnect.

One embodiment disclosed herein includes method for forming a multijunction solar cell comprising: forming a plurality of nanostructures,the plurality of nanostructures having first regions of a firstconductivity type and second regions of a second conductivity type toform first p-n junctions, the plurality of nanostructures having thirdregions of the first conductivity type and fourth regions of the secondconductivity type to form second p-n junctions; and forming a bi-layerelectrical interconnect having a first material in electrical andphysical contact with the second regions and a second material inelectrical and physical contact with the third regions, the firstmaterial and the second material are in electrical contact with eachother to allow charge to flow between the second regions and the thirdregions through the bi-layer electrical interconnect.

One embodiment disclosed herein includes a multi junction solar cellcomprising: an array of nanostructures, nanostructures in the array ofnanostructures having a plurality of photo-active regions, eachphoto-active regions is configured to absorb light of a different rangeof frequencies; and a bi-layer electrical interconnect providing a pathfor electrical current flow between adjacent ones of the photo-activeregions, each bi-layer electrical interconnect having a first layer thatmakes Ohmic contact with a p-type semiconductor and a second layer thatmakes Ohmic contact with an n-type semiconductor.

One embodiment disclosed herein includes an optoelectronic devicecomprising a plurality of nanostructures, the plurality ofnanostructures having first regions of a first conductivity type andsecond regions of a second conductivity type associated with firstphoto-active junctions, the plurality of nanostructures having thirdregions of the first conductivity type, the second regions and thirdregions are associated with second photo-active junctions; a firstelectrical contact in electrical contact with the first regions; asecond electrical contact in electrical and physical contact with thesecond regions; a third electrical contact in electrical contact withthe third regions; and logic coupled to the first electrical contact,the second electrical contact, and the third electrical contact, thelogic controls the first photo-active junctions independently of thesecond photo-active junctions.

One embodiment disclosed herein includes a method of operating anoptoelectronic device that includes a plurality of nanostructures, theplurality of nanostructures having first regions of a first conductivitytype and second regions of a second conductivity type to form firstphoto-active junctions, the plurality of nanostructures having thirdregions of the first conductivity type that form second photo-activejunctions with the second regions, a first electrical contact inelectrical contact with the first regions, a second electrical contactin electrical and physical contact with the second regions, a thirdelectrical contact in electrical contact with the third regions. Themethod comprises: controlling the first photo-active junctions to eithergenerate or detect light of a first range of wavelengths; andcontrolling the second photo-active junctions to either generate ordetect light of a second range of wavelengths, controlling the firstphoto-active junctions and the second photo-active junctions areperformed independently of each other.

One embodiment disclosed herein includes a method of forming anoptoelectronic device, the method comprising: forming a plurality ofnanostructures, the plurality of nanostructures having first regions ofa first conductivity type and second regions of a second conductivitytype to form first photo-active junctions, the plurality ofnanostructures having third regions of the first conductivity type thatform second photo-active junctions with the second regions; forming afirst electrical contact in electrical contact with the first regions;forming a second electrical contact in electrical and physical contactwith the second regions; forming a third electrical contact inelectrical contact with the third regions; and providing logic coupledto the first electrical contact, the second electrical contact, and thethird electrical contact, the logic controls the first photo-activejunctions independently of the second photo-active junctions.

One embodiment disclosed herein includes an optoelectronic devicecomprising: a nanostructure array, the nanostructures having sidewalls,groups of one or more nanostructures in the array forming pixels; afirst group of electrical contacts physically and electrically connectedto the sidewalls, the first group of electrical contacts are aligned ina first direction; and a second group of electrical contacts physicallyand electrically coupled to the sidewalls, the second group ofelectrical contacts are aligned in a second direction that is orthogonalto the first direction; wherein the pixels are individually controllableby applying appropriate voltages to the first group of electricalcontacts and to the second group of electrical contacts.

One embodiment disclosed herein includes a method of operating anoptoelectronic device that includes a nanostructure array, groups of oneor more nanostructures in the array forming pixels having at least twosub-pixels, the method comprising: controlling first sub-pixels togenerate or detect light of a first range of wavelengths; andcontrolling second sub-pixels to generate or detect light of a secondrange of wavelengths. The first and second sub-pixels are controlledindependently.

In the foregoing specification, several examples have been provided inwhich active regions of devices are associated with p-type and n-typeregions. Note that there may be an unintentionally doped region betweenthe type and n-type regions. Also note that p-type and n-type regionsmay be switched with suitable adjustments to operation of the device(such as reversing the polarity of applied voltages). Further note thatexample shapes of nanostructures having been depicted for illustrativepurposes. However, other shapes are possible. Thus, embodiments are notto be limited to columnar shapes, for example. Also note that differentshaped tops of nanostructures have been provided for illustration. Othertop shapes are possible.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Thus, the sole and exclusive indicatorof what is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

What is claimed is:
 1. An optoelectronic device comprising: a pluralityof nanostructures, the nanostructures including photo-active regions,the plurality of nanostructures having tops, bottoms, and sidewalls; abottom electrical contact in electrical contact with the bottoms of theplurality of nanostructures; and a top electrical contact in electricaland physical contact with sidewalls of the plurality of nanostructures,wherein the top electrical contact leaves a top portion of the pluralityof nanostructures exposed to allow light to enter or leave the pluralityof nanostructures from the tops of the plurality of nanostructureswithout passing through the top electrical contact.
 2. Theoptoelectronic device of claim 1, wherein the top electrical contactincludes a metal.
 3. The optoelectronic device of claim 1, wherein thetop electrical contact is opaque to light having a wavelength that isabsorbed or generated by the photo-active regions.
 4. The optoelectronicdevice of claim 1, wherein the top electrical contact is formed from adifferent material than the plurality of nanostructures.
 5. Theoptoelectronic device of claim 1, wherein a portion of the sidewalls ofthe nanostructures is above the top electrical contact.
 6. Theoptoelectronic device of claim 1, wherein the top electrical contactcompletely fills spaces between the plurality of nanostructures at alevel near the tops of the nanostructures.
 7. The optoelectronic deviceof claim 1, wherein the device includes a plurality of the topelectrical contacts.
 8. The optoelectronic device of claim 1, whereineach of the plurality of nanostructures further includes a p-typesemiconductor region and an n-type semiconductor region, wherein the topelectrical contact provides an electrical contact with either the p-typesemiconductor regions or the n-type semiconductor regions, the bottomelectrical contact provides an electrical contact to the other of thep-type semiconductor regions or the n-type semiconductor regions.
 9. Theoptoelectronic device of claim 1, wherein the top electrical contactforms an Ohmic contact with the plurality of nano structures.
 10. Theoptoelectronic device of claim 1, wherein the top electrical contactforms a Schottky contact with the plurality of nanostructures.
 11. Theoptoelectronic device of claim 1, wherein the plurality ofnanostructures have photo-active regions above the top electricalcontact.
 12. The optoelectronic device of claim 1, further comprisingone or more additional electrical contacts in electrical and physicalcontact with the sidewalls of the plurality of nano structures.
 13. Theoptoelectronic device of claim 1, wherein the bottom electrical contactis in physical contact with sidewalls of the plurality ofnanostructures.
 14. The optoelectronic device of claim 13, wherein eachof the plurality of nanostructures includes at least two p-n junctions.15. The optoelectronic device of claim 1, wherein the optoelectronicdevice is a solar cell.
 16. The optoelectronic device of claim 1,wherein the optoelectronic device is a light emitting diode.
 17. Theoptoelectronic device of claim 1, wherein the optoelectronic device is aphoto-detector.
 18. The optoelectronic device of claim 1, furthercomprising: logic that applies a bias voltage across the bottomelectrical contact and the top electrical contact to bias thephoto-active regions.
 19. The optoelectronic device of claim 1, furthercomprising: a first electrical lead that is electrically coupled to thebottom electrical contact; and a second electrical lead that iselectrically coupled to the top electrical contact, the first and secondelectrical leads for producing an output of the optoelectronic device inresponse to light absorbed near the photo-active regions.
 20. A methodfor forming an optoelectronic device comprising: forming a plurality ofnanostructures, the nanostructures including photo-active regions, theplurality of nanostructures having tops, bottoms, and sidewalls; forminga bottom electrical contact in electrical contact with the bottoms ofthe plurality of nano structures; and forming a top electrical contactin electrical and physical contact with sidewalls of the plurality ofnanostructures, wherein the top electrical contact leaves a top portionof the plurality of nanostructures exposed to allow light to enter orleave the plurality of nanostructures from the tops of the plurality ofnanostructures without passing through the top electrical contact. 21.The method for forming an optoelectronic device of claim 20, whereinforming a top electrical contact includes: depositing a metal such thatit covers the tops of the nanostructures; depositing a planarizingmaterial over the metal; etching back the planarizing material to revealportions of the metal over the tops of the nanostructures, some of theplanarizing material remains over spaces between the nanostructures;etching back the metal to reveal the tops of the nanostructures;removing any remaining planarizing material; and etching back the metalfurther to form the top electrical contact.
 22. The method for formingan optoelectronic device of claim 20, wherein forming a top electricalcontact includes: angle depositing metal on top portions of thenanostructures; and etching back the metal to form the top electricalcontact.
 23. The method for forming an optoelectronic device of claim22, further comprising: depositing a planarizing material over the metalafter angle depositing the metal; etching back the planarizing materialto reveal portions of the metal over the tops of the nanostructures,some of the planarizing material remains over spaces between thenanostructures; etching back the metal to reveal the tops of thenanostructures; and removing any remaining planarizing material.
 24. Themethod for forming an optoelectronic device of claim 20, wherein formingthe plurality of nanostructures includes forming a p-type semiconductorregion and an n-type semiconductor region in each of the plurality ofnanostructures, wherein the top electrical contact provides anelectrical contact with either the p-type semiconductor regions or then-type semiconductor regions, the bottom electrical contact provides anelectrical contact to the other of the p-type semiconductor regions orthe n-type semiconductor regions.
 25. The method for forming anoptoelectronic device of claim 20, wherein forming the top electricalcontact includes forming the top electrical contact with a material thatprovides an Ohmic contact with the plurality of nano structures.
 26. Themethod for forming an optoelectronic device of claim 20, wherein formingthe top electrical contact includes forming the top electrical contactwith a material that provides a Schottky contact with the plurality ofnanostructures.
 27. The method for forming an optoelectronic device ofclaim 20, wherein forming the plurality of nanostructures includesforming photo-active regions above the top electrical contact.
 28. Themethod for forming an optoelectronic device of claim 20, furthercomprising forming one or more additional electrical contacts inelectrical and physical contact with other portions of the sidewalls ofthe plurality of nanostructures.
 29. The method for forming anoptoelectronic device of claim 20, wherein forming the plurality ofnanostructures includes forming a plurality of p-type semiconductorregions and a plurality of n-type semiconductor regions in each of theplurality of nanostructures.
 30. The method for forming anoptoelectronic device of claim 20, wherein forming a bottom electricalcontact in electrical contact with the bottoms of the plurality ofnanostructures includes forming metal in contact with the sidewalls ofthe nanostructures.
 31. An optoelectronic device comprising: an array ofnanostructures formed from a material that includes one or moresemiconductors, the nanostructures including one or more p-n junctions,the nanostructures including photo-active regions associated with thep-n junctions, the nanostructures having tops, bottoms, and sidewalls,the nanostructures have spaces between them; a bottom electrical contactin electrical contact with the bottoms of the nanostructures; and a topelectrical contact in electrical and physical contact with the sidewallsof the nanostructures, wherein the top electrical contact issubstantially opaque to light having a wavelength that is absorbed orgenerated by the photo-active regions.
 32. The optoelectronic device ofclaim 31, wherein the top electrical contact completely fills the spacesbetween the nanostructures at a level near the tops of thenanostructures.
 33. The optoelectronic device of claim 31, wherein thetop electrical contact includes a metal.
 34. An optoelectronic devicecomprising: a plurality of nanostructures, the nanostructures includingp-n junctions, the plurality of nanostructures having tops, bottoms, andsidewalls; a first electrical contact in electrical contact with thesidewalls of the plurality of nanostructures, the first electricalcontact is on a first side of the p-n junctions; and a second electricalcontact in electrical and physical contact with sidewalls of theplurality of nanostructures, the second electrical contact is on asecond side of the p-n junctions that is opposite the first side, thesecond electrical contact is a top electrical contact, wherein the topelectrical contact leaves a top portion of the plurality ofnanostructures exposed to allow light to enter or leave the plurality ofnanostructures from the tops of the plurality of nanostructures withoutpassing through the top electrical contact, the first electrical contactand second electrical contact are together either an input or an outputof the optoelectronic device.